This invention relates to the field of medical devices for the introduction and removal of fluids from a patient. More particularly, the invention relates to catheters and a method of manufacturing catheters for use with a needle.
Medical devices, such as intravenous (IV) catheters, have been developed for insertion into the tissues of a body cavity of a patient to introduce or remove fluids. Such devices are most commonly intended for intravascular use, particularly for infusion of normal intravenous solutions, including antibiotics and other drugs, although various other uses are quite common. IV catheters are also used to withdraw blood from the patient for normal blood-gas analysis as well as other blood work. While IV catheters are available in several different types, one common type of catheter is constructed so as to be mounted coaxially upon a relatively long, hollow needle or cannula with a slight friction fit, referred to herein as an xe2x80x9cover-the-needlexe2x80x9d arrangement. A hub is attached at one end of the catheter and is designed so as to be connectable with and detachable from an IV fluid supply line. To insert the catheter into the patient, the needle and catheter together are inserted through the patient""s skin, whereupon the needle may be withdrawn, leaving the catheter in place.
Since the catheter will normally be left in position for at least several hours, it must be flexible and efficiently shaped for the introduction of fluid or removal of fluid. The shape of the catheter tip must produce minimal trauma to the patient during insertion of the catheter into the patient and while the catheter is in place in the patient. A tip shape that provides these characteristics has a tapered outer wall and an angled tip and is disclosed in U.S. Pat. No. 4,588,398, incorporated herein by reference. A process for making such a catheter tip is disclosed in U.S. Pat. No. 4,661,300, incorporated herein by reference. In this process, the catheter is placed on a mandrel. A die having an interior molding surface, which is tapered according to the tip desired on the catheter, is aligned axially with the mandrel. The die is heated, typically using RF energy, thereby heating the catheter tip so that it becomes flowable. The mandrel and die are brought together so the distal edge of the mandrel engages the tapered portion of the die. This action cleanly forms a smooth and uniform tapered tip for the catheter but has not been designed specifically to address formation of the internal geometry of the catheter and is incapable of achieving the preferred geometry of the instant invention.
Catheters must be designed of materials and to have shapes that are rigid enough to pass through the tissue of the patient and yet soft enough to avoid discomfort and tissue trauma to the patient when in place. During insertion, the forces exerted on the flexible catheter by the patient""s tissue may cause a xe2x80x9cpeeling backxe2x80x9d of the catheter, preventing the catheter from full insertion into the patient""s vein. This problem can be compounded when the needle and catheter must be inserted into a septum of an implantable infusion port (such ports may be implanted in a patient for long term vascular access). These ports may provide a higher resistive force than human tissue. Consequently, the catheter, particularly its tip, must include some structural rigidity.
Concerns for safety have driven the development of devices that capture the tip of a needle within a container of some sort. See, e.g., U.S. Pat. No. 6,004,294 and U.S. application Ser. No. 09/717,148, filed Nov. 21, 2000, both incorporated herein by reference. In certain such systems, it is advantageous to have a discontinuity, such as a bump or annular ring, on the needle, near the tip, to be grasped and held by the closed container (preventing the needle from exiting the container). However, prior art systems for forming catheters may result in inconsistent internal catheter geometry that interferes with the insertion of the needle into the catheter. Consequently, the tip of the needle cannot always be positioned at a specific desired location beyond the tip of the catheter. Further, even if positioned correctly, the inconsistent formation of catheters may result in an inconsistent (and thus undesirable) force to remove the needle from the catheter once in position.
It is therefore an advantage of an aspect of this invention to provide a catheter and a method of making catheters that can be efficiently inserted into patients, including into septums implanted within patients, with minimal patient discomfort and left in patients while minimizing any vascular trauma.
It is an advantage of another aspect of the invention to provide a catheter and a method of making a catheter that can be employed consistently with a needle having a discontinuity near the needle tip.
It is an advantage of yet another aspect of the invention to provide a catheter and a method of making a catheter that can be inserted into a patient""s tissue or a septum without pealing back off the needle.
The above and other advantages and objects of the invention will be apparent upon consideration of the following description.
In accord with one aspect of the invention, a method is provided for forming a catheter for insertion into a patient""s skin. A flexible, biocompatible material is extruded into a tube. The tube has an inner wall defining a substantially constant inner cross-section, an outer wall defining a substantially constant outer cross-section and an axis. A lumen is defined by the inner wall and extends co-axially within the tube from a proximal portion, through a distal portion to a distal face, forming an opening in the distal face of the tube. A mandrel is provided that has a body portion and a tip portion. The body portion has a larger cross-section than the tip portion. Typically, the body portion has a cross-section that is the same as or less than the inner cross-section of the tube. The mandrel is inserted into the lumen such that the tip portion of the mandrel is disposed in the distal portion of the tube proximate to the distal face of the tube. The distal portion of the tube is deformed such that the outer wall tapers inward toward the opening and the inner wall conforms to the tip portion of the mandrel. The portion of the tube""s inner wall that has conformed to the tip portion of the mandrel defines a catheter land having a predetermined cross-section substantially matching the cross-section of the tip portion and a predetermined length. The catheter is cured and the mandrel is withdrawn from the lumen.
Certain implementations of this aspect of the invention provide that the material of the tube is thermoplastic and is deformed by heating in a hot die. Other plastic materials may be employed and may be formed as necessary, including any required curing steps, to achieve the desired geometry. The mandrel may be positioned so that the free end of the mandrel is co-located with the distal opening in the tube, or so that the free end extends through the distal opening. The tip portion of the mandrel may have various shapes to impart a desired geometry to the catheter land, such as grooves to form ridges in the land, or a conical shape to form a conical land. Such ridges may be employed to direct the tearing of a catheter when use as a splittable introducer, such as disclosed in U.S. Pat. Nos. 6,080,141, 6,027,480 and 6,273,871, each incorporated herein by reference. The needle itself may be used as the mandrel, and may be heated to assist forming the catheter.
In accord with another aspect of the invention, an over-the-needle catheter assembly is provided including a tube made of a flexible, biocompatible material. The tube has a proximal portion, a distal portion and a catheter tip positioned on the distal portion remote from the proximal portion. A lumen extends through the tube, substantially co-axially with the tube, from the proximal portion, through the distal portion and through to the catheter tip. The lumen has a proximal cross-section in the proximal portion of the tube and a distal cross-section in the distal portion of the tube. The proximal cross-section is larger than the distal cross-section. A shoulder is disposed in the tube between the distal portion and the proximal portion. A catheter land, having a predetermined length, is defined as the portion of the lumen disposed in the distal portion of the tube between the shoulder and the distal end. A needle is disposed in the lumen and has a substantially circular cross-section. A discontinuity is located on the needle at a predetermined position with respect to the needle tip. The distance between the distal edge of the discontinuity and the needle tip is substantially equal to the length of the catheter land. The discontinuity is sized such that it fits within the lumen at the proximal portion but does not fit within the lumen at the distal portion.
Certain implementations of this aspect of the invention provide that the shoulder is disposed at a selected angle with respect to the axis of the lumen.